With the progress of dense wavelength division multiplexing (DWDM) technology and the development of optical amplifiers (OA), the capacity of optical communications networks is growing and the optical power level in optical links has also increased. Current optical amplifiers used for long haul telecommunications can launch 200-400 mW (milliwatts) of optical power into single mode fibers and next generation systems are expected to reach levels approaching 1 W (1 Watt or 1000 milliwatts). In addition, for current fiber to the premises (FTTP) technology using passive optical networks (PON), the optical power for analog video transport at 1550 nm (nanometers), is 200 mW. At these power levels, radiation safety issues become significant. Accidental cable or fiber breaks and uncoupled or opened connectors may expose the human body to invisible infra-red radiation and cause damage depending on exposure time.
Some of the conventional optical power transport systems include an automatic laser shut-off feature to avoid exposure to radiation. The laser or amplifier power is shut-off at the transmitting end when the optical signal at the receiving end is lost and an optical supervisory channel (OSC) cannot establish communications between the two ends. Although conventional shut-off features may work in cases of a fiber break or an open connector, conventional shut-off devices may be activated by a lossy element of the system or a malfunctioning receiver or OSC. Therefore conventional shut-off features may shut-off the laser or amplifier power unnecessarily. Moreover, conventional shut-off devices cannot provide early detection of increasing reflection levels in the fiber link, which interfere with the transmitted signal, creating phase noise that is converted to intensity noise that degrades the transmitted signal quality.